A magnetoresistance device is a type of memory device in which data can be stored as an alterable orientation of magnetization. As one example, in FIGS. 1a and 1b, a prior tunneling magnetoresistance (TMR) device 200 includes a reference layer 212 (also referred to as a pinning film or pinned layer) that includes a pinned orientation of magnetization M1 that is fixed in a predetermined orientation, a data layer 210 that includes an alterable orientation of magnetization M2 that can be altered by an external magnetic field, and a thin tunnel barrier layer 211 that separates the data layer 210 from the reference layer 212.
A state of the data stored in the data layer 210 is determined by an orientation of the alterable orientation of magnetization M2 relative to the pinned orientation of magnetization M1. For example, if the alterable orientation of magnetization M2 is oriented in the same direction as the pinned orientation of magnetization M1 (e.g. parallel as in FIG. 1a), then a logic “1” is stored in the data layer 210. On the other hand, if the alterable orientation of magnetization M2 is oriented in a direction opposite that of the pinned orientation of magnetization M1 (e.g. anti-parallel as in FIG. 1b), then a logic “0” is stored in the data layer 210.
For the TMR device 200, the state of the data stored in the data layer 210 is determined by measuring or sensing a tunneling resistance across the data and reference layers (210, 212). One value of resistance is indicative of the logic “1” and a different value of resistance is indicative of the logic “0”. It is desirable to have the value of resistance for the logic “1” be as far apart as possible from the value of resistance for the logic “0”. The further apart those two values are, the higher a signal-to-noise ratio ΔR/R of the TMR device 200. The ΔR is a change in resistance from a logic “1” to a logic “0” or vice-versa and R is a lower of the two resistance values for a logic “1” and a logic “0”. A high signal-to-noise ratio allows for accurate sensing of the data in the data layer 210 during a read operation to the TMR device 200. Accurate sensing is a necessity if the TMR device 200 is to be used for data storage (e.g. as a MRAM device). A low signal-to-noise ratio is undesirable because the value of resistance for the logic “0” is not different enough from the value of resistance for the logic “1”; therefore, the state of the data cannot be accurately determined and the TMR device will not be suitable as a memory device for data storage.
In FIGS. 2a and 2b, a plurality of thin film layers of material are required to form the prior TMR device 200. The layers used will depend on a selected topology for the TMR device 200. Typically, the layers are only a few nanometers thick. For example, the tunnel barrier layer 211 can be 1.0 nm thick or less. The data and reference layers (210, 212) can be 10 nm thick or less. The tunnel barrier layer 211 can be made from a dielectric material, such as aluminum oxide (Al2O3), for example. The data and reference layers (210, 212) can be made from one or more layers of a ferromagnetic material. Examples of materials for the data layer 210 include nickel-iron (NiFe) or a sandwich of nickel-iron:colbalt-iron (NiFe:CoFe). Examples of materials for the reference layer 212 include a sandwich of cobalt-iron:ruthenium:cobalt-iron (CoFe:Ru:CoFe) or nickel-iron (NiFe).
One disadvantage of prior the TMR device 200 is that a topology of the TMR device 200 can include a pinning film 214 that is adjacent to the reference layer 212 and is operative to prevent rotation of the pinned orientation of magnetization M1 in response to an external magnetic field (e.g. write currents). The pinning film 214 can be made from a material that includes manganese (Mn), such as IrMn, PtMn, and MnFe, for example. The manganese (Mn) in the pinning film 214 can diffuse (see dashed arrows D) across an interface I between the pinning film 214 and the reference layer 212, particularly at high processing temperatures (e.g. ≧400° C.) that are required to integrate magnetoresistance devices with CMOS circuitry to form a data storage device (e.g. MRAM). The diffusion D of the Mn into the reference layer 212 at those high processing temperatures results in a low signal-to-noise ratio ΔR/R and the low signal-to-noise ratio ΔR/R renders the device useless for data storage purposes. Solutions to the diffusion problem include not using a high temperature CMOS process or providing a diffusion barrier between the pinning film 214 and the reference layer 212 to prevent the diffusion D of the Mn across the interface I. At present, it is not possible to eliminate CMOS circuitry and the high temperatures incumbent to the CMOS fabrication process.
Cobalt (Co) has been found to be an effective Mn diffusion barrier. Prior methods for depositing the Co include sputtering deposition processes that are well understood in the microelectronics art. Unfortunately, in standard sputtering deposition systems the coverage of the Co material is not uniform across the layer the Co is deposited on. Metals (e.g. Co) tend to form island growth, and then coalesce into a continuous film. However, Co has a high saturation magnetization and can therefore impart a large antiferromagnetic coupling to magnetic memory element.
Another solution is to use an artificial antiferromagnet which does not contain Mn; however, artificial antiferromagnet structures require huge magnetic field anneals to set their magnetic state. Obtaining such a large magnetic field across a semiconductor wafer of 8.0 inches or more in diameter is prohibitively expensive. Another solution is to leave a bottom conductor of the magnetic memory element unpatterned; however, an unpatterned conductor increases a probability of reduced device yields due to shorting.
Accordingly, a method for depositing a very thin layer of material for a Mn diffusion barriers is desired. Atomic layer deposition (ALD), used primarily in the semiconductor industry, is one prior method for depositing thin layers of material. ALD is a reactive deposition method as opposed to a direct deposition method. For some materials ALD requires a water precursor, which can be destructive to device materials and/or properties, especially in materials that are susceptible to corrosion, such as the ferromagnetic materials in a TMR junction. ALD creates uniform thin film layers with very controllable thickness; however, the deposited layer is conformal to the underlying topography. If the topography is non-uniform, defects such as asperities and pinholes can result in breaches in the diffusion barrier through which the Mn can diffuse into the reference layer 212.
Consequently, there exists a need for a method of fabricating a manganese diffusion barrier at an interface in a magnetoresistance device. There is also a need for a method of fabricating a manganese diffusion barrier at an interface in a magnetoresistance device that can create a uniform interface surface upon which to deposit the manganese diffusion barrier. Finally, there is a need for a method of fabricating a manganese diffusion barrier that produces a very thin and uniform diffusion barrier on an interface surface.